Imo, 23 or 24 is too cold.. depend your coral origin from where.. our region about 26. So no need to go 23 or 24. Can save up electricity also ma. My 2 cent worth.
May be the heat from his chiller heat up the sump wate coz as I see most heat will trap inside the cabinet even though the door leave it open.so the water will not reach the desire temperature and the chiller keep running lo. My own opinion.
Selling all as a set. 400/-. Arrange own transport.
Main tank 2 sided are crystal glass. 1.5 ft cube normal glass. Both tank less than a year. Cabinet about 2.5 years.